1. Field of the Invention
This invention relates to a method for producing a hose having low permeability.
2. Description of the Related Art
In an air conditioner such as one for use in an automobile, a compressor, a condensor and an evaporator are interconnected by hoses through which a refrigerant such as FREON refrigerant circulates. To circulate such a refrigerant at high temperature and under high pressure, the hoses must be formed of a material having high durability, anticorrosion, and heat resistance, and also low permeability to prevent the refrigerant from permeating them.
Methods for producing a hose for transferring a refrigerant are disclosed in, for example, Published Examined Japanese Patent Application No. 63-45302 and Published Unexamined Japanese Patent Application No. 1-271229.
In the method disclosed in Published Examined Japanese Patent Application No. 63-45302, molten resin is, at first, extruded from an extruder, and then coated onto the outer surface of a mandrel heated above 40.degree. C. but below the melting point of the resin. The molten resin is then cooled down, thereby forming an inner pipe. A reinforcing layer, a rubber layer as an outer pipe, and the like are coated on the outer surface of the inner resin pipe. The inner resin pipe, reinforcing layer, and outer rubber pipe are cured to prevent the inner resin pip from being cooled abruptly and hence to restrain the deformation of the outer surface of the inner pipe.
The method disclosed in Published Unexamined Japanese Patent Application No. 1-271229 is similar to the above-described method. This method employs a mandrel made of rubber or resin whose plasticizer content is within a range of 0 to 10% by weight, and whose bending force is within a range of 0.2 to 3 kgf. A releasing agent is applied to the mandrel, and then the mandrel is dried and coated with molten resin. Thereafter, the mandrel is removed from the resultant hose such that the hose does not have flaws in its inner surface, so as to prevent gas leakage.
The above method comprises the steps of:
i) extruding molten resin from a resin extruder onto a mandrel, thereby forming a resin layer;
ii) applying an adhesive to the resin layer, thereby forming an adhesive layer;
iii) extruding rubber from a rubber extruder and coating it onto the adhesive layer, thus forming an inner rubber layer;
iv) braiding the outer peripheral surface of the inner layer, thereby forming a reinforcing layer;
v) extruding rubber from the rubber extruder and coating it onto the reinforcing layer, thus forming an outer rubber layer;
vi) wrapping the outer peripheral surface of the outer layer with a tape;
vii) curing the resultant structure;
viii) removing the tape wrapped; and
ix) removing the mandrel by applying pressurized water between the mandrel and resin layer.
In this method, however, the resin layer is likely to stick to the outer surface of the mandrel too firmly to remove the mandrel in the last step, thereby making flaws in the inner surface of the resin layer when the mandrel is removed, which may cause leakage of refrigerant.
Further, if highly-pressurized water is applied between the mandrel and resin layer to facilitate the removal of the mandrel, it causes the resin layer to expand locally and thus to have some thin portions through which refrigerant may leak.